Functional status of STAT3 and MAPK3/1 signaling pathways in granulosa cells during bovine follicular deviation

DNA Methylation Mediates the Transcription of STAT4 to Regulate KISS1 During Follicular Development

Maturation of follicles is the primary condition for the initiation of puberty, and excessive apoptosis of granulosa cells (GCs) will hinder the normal development of follicles in pigs. Signal Transducer and Activator of Transcription 4 (STAT4) plays an important role in cell proliferation and apoptosis. However, the mechanism of DNA methylation regulating STAT4 transcription and affecting follicle development in pigs remains unclear. To resolve this problem, we constructed a STAT4 overexpression vector and interference fragment to explore the effects of STAT4 on GC function and investigate the effects of changes in methylation status of the STAT4 promoter region on cell function and kisspeptin-1 (KISS1) expression, as well as the STAT4 effects on the development of the follicles of pigs and mice in vitro. We found that the expression of STAT4 decreased, while DNA methylation of the STAT4 promoter region increased with the growth of the follicles. After overexpression of STAT4, the apoptosis of GCs was increased but the proliferation, cell cycle and estrogen secretion of GCs were inhibited. When GCs were treated with DNA methyltransferase inhibitor (5-Aza-CdR), the methylation of the STAT4 promoter region decreased, resulting in a significant increase in the expression of STAT4. Consequently, the expression of KISS1 was inhibited. At the same time, the expressions of genes related to cell proliferation, cell cycle and estrogen secretion signaling pathways decreased, while the expressions of genes related to the apoptosis signaling pathway increased. After infection with the STAT4 lentiviral vector (LV-STAT4) in follicles of mice, the expression of STAT4 in ovaries of mice significantly increased, and the expression of KISS1 was significantly decreased. The capillaries on the surface of follicles were constricted, the age of puberty onset in mice was delayed while the levels of GnRH, LH, FSH and E2 in serum were decreased. In conclusion, we found that reduced methylation status of the STAT4 promoter region promoted the transcription of STAT4 and then inhibited the expression of KISS1, as well as promoted the apoptosis of GCs and ultimately inhibited the normal development of follicles in mammals.

Sheep litter size heredity basis using genome-wide selective analysis

Sheep are important herbivorous domestic animal globally, and the Chinese indigenous sheep breed has a multitude of economically significant variations due to the diverse geographical and ecological conditions. In particular, certain native breeds exhibit a visible high litter size phenotype due to the selection pressure of natural and artificial for thousands of years, offering an ideal animal model for investigating sheep's fecundity. In this study, selective signal analysis was performed on public whole-genome sequencing data from 60 sheep across eight breeds to identify candidate genes related to litter size. Results revealed that a total of 34,065,017 single-nucleotide polymorphisms (SNPs) were identified from all sheep, and 65 candidate genes (CDGs) were pinpointed from the top 1% of interacted windows and SNPs between the pairwise fixation index (FST, >0.149543) and cross-population extended haplotype homozygosity (XP-EHH, >0.701551). A total of 41 CDGs (e.g. VRTN, EYA2 and MCPH1) were annotated to 576 GO terms, of which seven terms were directly linked to follicular and embryonic development (e.g. TBXT, BMPR1B, and BMP2). In addition, 73 KEGG pathways were enriched by 21 CDGs (e.g. ENTPD5, ABCD4 and RXFP2), mainly related to Hippo (TCF4, BMPR1B and BMP2), TGF-β (BMPR1B and BMP2), PI3K-Akt (ITGB4, IL4R and PPP2R5A) and Jak-STAT signalling pathways (IL20RA and IL4R). Notably, a series of CDGs was under strong selection in sheep with high litter size traits. These findings result could improve the comprehension of the genetic underpinnings of sheep litter size. Furthermore, it provides valuable CDGS for future molecular breeding.

Janus Kinase 3 phosphorylation and the JAK/STAT pathway are positively modulated by follicle-stimulating hormone (FSH) in bovine granulosa cells

Janus kinase 3 (JAK3) is a member of the JAK family of tyrosine kinase proteins involved in cytokine receptor-mediated intracellular signal transduction through the JAK/STAT signaling pathway. JAK3 was previously shown as differentially expressed in granulosa cells (GC) of bovine pre-ovulatory follicles suggesting that JAK3 could modulate GC function and activation/inhibition of downstream targets. We used JANEX-1, a JAK3 inhibitor, and FSH treatments and analyzed proliferation markers, steroidogenic enzymes and phosphorylation of target proteins including STAT3, CDKN1B/p27^Kip1 and MAPK8IP3/JIP3. Cultured GC were treated with or without FSH in the presence or not of JANEX-1. Expression of steroidogenic enzyme CYP11A1, but not CYP19A1, was upregulated in GC treated with FSH and both were significantly decreased when JAK3 was inhibited. Proliferation markers CCND2 and PCNA were reduced in JANEX-1-treated GC and upregulated by FSH. Western blots analyses showed that JANEX-1 treatment reduced pSTAT3 amounts while JAK3 overexpression increased pSTAT3. Similarly, FSH treatment increased pSTAT3 even in JANEX-1-treated GC. UHPLC-MS/MS analyses revealed phosphorylation of specific amino acid residues within JAK3 as well as CDKN1B and MAPK8IP3 suggesting possible activation or inhibition post-FSH or JANEX-1 treatments. We show that FSH activates JAK3 in GC, which could phosphorylate target proteins and likely modulate other signaling pathways involving CDKN1B and MAPK8IP3, therefore controlling GC proliferation and steroidogenic activity.

Influence of Estrus on Dairy Cow Milk Exosomal miRNAs and Their Role in Hormone Secretion by Granulosa Cells

Estrus is crucial for cow fertility in modern dairy farms, but almost 50% of cows do not show the behavioral signs of estrus due to silent estrus and lack of suitable and high-accuracy methods to detect estrus. MiRNA and exosomes play essential roles in reproductive function and may be developed as novel biomarkers in estrus detection. Thus, we analyzed the miRNA expression patterns in milk exosomes during estrus and the effect of milk exosomes on hormone secretion in cultured bovine granulosa cells in vitro. We found that the number of exosomes and the exosome protein concentration in estrous cow milk were significantly lower than in non-estrous cow milk. Moreover, 133 differentially expressed exosomal miRNAs were identified in estrous cow milk vs. non-estrous cow milk. Functional enrichment analyses indicated that exosomal miRNAs were involved in reproduction and hormone-synthesis-related pathways, such as cholesterol metabolism, FoxO signaling pathway, Hippo signaling pathway, mTOR signaling pathway, steroid hormone biosynthesis, Wnt signaling pathway and GnRH signaling pathway. Consistent with the enrichment signaling pathways, exosomes derived from estrous and non-estrous cow milk both could promote the secretion of estradiol and progesterone in cultured bovine granulosa cells. Furthermore, genes related to hormonal synthesis (CYP19A1, CYP11A1, HSD3B1 and RUNX2) were up-regulated after exosome treatment, while exosomes inhibited the expression of StAR. Moreover, estrous and non-estrous cow-milk-derived exosomes both could increase the expression of bcl2 and decrease the expression of p53, and did not influence the expression of caspase-3. To our knowledge, this is the first study to investigate exosomal miRNA expression patterns during dairy cow estrus and the role of exosomes in hormone secretion by bovine granulosa cells. Our findings provide a theoretical basis for further investigating milk-derived exosomes and exosomal miRNA effects on ovary function and reproduction. Moreover, bovine milk exosomes may have effects on the ovaries of human consumers of pasteurized cow milk. These differential miRNAs might provide candidate biomarkers for the diagnosis of dairy cow estrus and will assist in developing new therapeutic targets for cow infertility.

miR-122-5p regulates proliferation and apoptosis of chicken granulosa cells of hierarchal follicles by targeting MAPK3

Chicken follicles plays a crucial role in the reproductive performance, especially in laying period. Recently, miR-122-5p has been found to be differentially expressed in the ovaries of rats with polycystic ovary syndrome and normal rats, indicating the potential role of miR-122-5p in the development of granulosa cells (GCs). In present study, we found that miR-122-5p was highly expressed in chicken atrophic ovaries. Herein, we investigated its function on GC proliferation and apoptosis of chicken in vitro. We found that overexpression of miR-122-5p significantly inhibited proliferation and promoted apoptosis of GCs, whereas the opposite effects were detected in miR-122-5p knockdown GCs. Meanwhile, mitogen-activated protein kinase 3 (MAPK3) was confirmed as a new target gene of miR-122-5p by bioinformatics software prediction and the dual-luciferase reporter assay verification. Furthermore, after knockdown of MAPK3, the function of MAPK3 for GC proliferation and apoptosis was opposite to that of miR-122-5p. Collectively, our results indicated that miR-122-5p impeded chicken GC proliferation and promoted apoptosis through the post-transcriptional downregulation of MAPK3.

Leukemia inhibitory factor prevents chicken follicular atresia through PI3K/AKT and Stat3 signaling pathways

Autophagy of granulosa cell (GC) may be a supplementary mechanism involved in follicular atresia through cooperating with apoptosis. Leukemia inhibitory factor (LIF) has been shown to promote follicular growth, through the underlying molecular mechanisms remain unclear. Rapamycin, an autophagy inducer, triggered the elevation of GC apoptosis within follicles, and then prevented follicular growth. However, combined treatment with LIF relieved the follicular regression caused by rapamycin, mainly resulting in alleviating the decline of GCs viability and cell autophagic apoptosis, and eventually, promoting follicle development. Further investigation revealed that LIF inhibited the GC autophagic apoptosis by activating PI3K/AKT and Stat3 pathways, reflecting an increase of BCL-2 expression but a decrease in BECN1. Additionally, blocking PI3K/AKT and Stat3 pathways resulted in the reduction of LIF protection against follicular atresia. These findings illustrated that LIF activated the PI3K/AKT and Stat3 signaling pathways to inhibit GC autophagic cell death, and further relieve chicken follicular atresia.

Hemodynamic, endocrine, and gene expression mechanisms regulating equine ovarian follicular and cellular development

Ovulatory follicle development and associated oocyte maturation involve complex coordinated molecular and cellular mechanisms not yet fully understood. This study addresses the relationships among follicle diameter, follicle wall blood flow, follicular-fluid factors, and gene expression for follicle growth, steroidogenesis, angiogenesis, and apoptosis in granulosa/cumulus cells and oocytes during different stages from the beginning of largest/ovulatory follicle to impending ovulation in mares. The most remarkable findings were (i) a positive association between follicle development, follicle blood flow, intrafollicular follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, progesterone, and messenger RNA (mRNA) expression for FSHR and LHCGR in granulosa cells of the largest/ovulatory follicle; (ii) a plateau or decrease in follicle diameter and blood flow and granulosa cell mRNA for FSHR, LHCGR, IGF1R, VEGFR2, CYP19A1, and CASP3 at the preovulatory stage; (iii) higher StAR and BCL2 and lower CASP3 mRNA in granulosa cells at the time of impending ovulation; (iv) greater IGF1R mRNA for granulosa cells at the predeviation stage; and (v) lower FSHR, LHCGR, IGF1R, and VEGFR2 mRNA in cumulus cells and greater LHCGR and IGF1R mRNA in oocytes at the ovulatory stage. This study is a critical advance in the understanding of molecular mechanisms of follicle development and oocyte maturation and is expected to be vital for future studies targeting potential markers.

Estrous cycle impacts microRNA content in extracellular vesicles that modulate bovine cumulus cell transcripts during in vitro maturation†

Extracellular vesicles (EVs) are nanoparticles secreted by ovarian follicle cells. Extracellular vesicles are an important form of intercellular communication, since they carry bioactive contents, such as microRNAs (miRNAs), mRNAs, and proteins. MicroRNAs are small noncoding RNA capable of modulating mRNA translation. Thus, EVs can play a role in follicle and oocyte development. However, it is not clear if EV contents vary with the estrous cycle stage. The aim of this study was to investigate the bovine miRNA content in EVs obtained from follicles at different estrous cycle stages, which are associated with different progesterone (P4) levels in the follicular fluid (FF). We collected FF from 3 to 6 mm follicles and evaluated the miRNA profile of the EVs and their effects on cumulus-oocyte complexes during in vitro maturation. We observed that EVs from low P4 group have a higher abundance of miRNAs predicted to modulate pathways, such as MAPK, RNA transport, Hippo, Cell cycle, FoxO, oocyte meiosis, and TGF-beta. Additionally, EVs were taken up by cumulus cells and, thus, affected the RNA global profile 9 h after EV supplementation. Cumulus cells supplemented with EVs from low P4 presented upregulated genes that could modulate biological processes, such as oocyte development, immune responses, and Notch signaling compared with genes of cumulus cells in the EV free media or with EVs from high P4 follicles. In conclusion, our results demonstrate that EV miRNA contents are distinct in follicles exposed to different estrous cycle stage. Supplementation with EVs impacts gene expression and biological processes in cumulus cells.

Prostaglandin F2α regulation and function during ovulation and luteinization in cows

Although prostaglandins are important in the ovulation process, a precise role for prostaglandin F2α (PGF) has not been elucidated. This study aimed to evaluate the regulation of PGF receptor mRNA (PTGFR) in granulosa cells and the local effect of PGF on ovulation and luteinization. In Experiment 1, using samples collected in vivo before (Day 2), during (Day 3) and after (Day 4) follicular deviation, expression of PTGFR in bovine granulosa cells was more abundant in the dominant follicle after deviation than in subordinates (P < 0.05). However, the expression of PTGFR was not regulated (P = 0.1) in preovulatory follicles at different time-points (0, 3, 6, 12 and 24 h) after ovulation induction with GnRH. In Experiment 2, to assess the role of systemic PGF treatment on luteinization and vascularization of preovulatory follicles, flunixin meglumine (FM), a nonsteroidal anti-inflammatory drug, was used to inhibit endogenous prostaglandin synthesis. Cows with preovulatory follicles were induced to ovulate with GnRH (0 h) and allocated to three groups: Control, with no further treatment; FM, treated with 2.2 mg/kg FM im 17 h after GnRH treatment; and FM + PGF, treated with FM 17 h after GnRH, followed by 25 mg dinoprost tromethamine (PGF) 23 h after GnRH treatment. FM injection was able to reduce the concentration of PGF in the follicular fluid (FF) (P < 0.001). However, contrary to our hypothesis, color Doppler ultrasound evaluations revealed decreased vascular flow in FM + PGF group (P < 0.05), and no effect of the treatments on intrafollicular P4 and E2 concentrations 24 h after GnRH. The prostaglandin metabolite (PGFM) concentrations in the FF were greater in cows receiving systemic PGF (P < 0.001), which prompted us to further check its role on ovulation. Therefore, in Experiment 3, in a final attempt to demonstrate the local effect of PGF on ovulation, cows with preovulatory follicles received an intrafollicular injection (IFI) of PBS (Control) or 100 ng/mL purified PGF (PGF group). PGF treatment did not affect the time of ovulation after IFI (66 ± 6.4 and 63 ± 8.5 h for control and PGF, respectively; P > 0.05), further suggesting that it has no direct effect in the ovulatory process. Based on our findings, we concluded that FM decreased PGF synthesis within the follicle, whereas PGF treatment decreased follicular vascularization. In addition, the in vivo model of intrafollicular injection evidenced that PGF alone is not able to locally induce ovulation.

Regulation and function of leptin during ovarian follicular development in cows

Although it is well documented that leptin signals the body nutritional status to the brain, mechanisms of leptin regulation at the ovary are not well understood. This study was conducted to determine whether there was leptin and the receptor for leptin (LEPR) in cattle ovarian follicles and to investigate potential actions of leptin on follicular growth in vivo and on regulation of granulosa cell functions in vitro. There was leptin and LEPR in granulosa and theca cells of dominant and subordinate follicles, with greater immunostaining for leptin in granulosa cells of subordinate follicles. There was a lesser relative abundance of leptin receptor gene-related protein (LEPROT) and of the adiponectin receptors 1 (ADIPOR1) and 2 (ADIPOR2) mRNA transcripts in granulosa cells of subordinate than dominant follicles (P < 0.05). Intrafollicular injection of either 100 or 1000 ng/mL leptin did not affect the diameter and the growth of dominant follicles (P> 0.05). Supplementation of in vitro culture medium with different leptin concentations did not affect (P > 0.05) the relative abundance of hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 (HSD3B1), cytochrome P450 family 11 subfamily A member 1 (CYP11A1), signal transducer and activator of transcription 3 (STAT3) and X-linked inhibitor of apoptosis protein (XIAP) mRNA transcripts in granulosa cells. These findings indicate that leptin and LEPR are present in the follicular cells of cattle ovaries, but leptin apparently does not have essential functions in steroidogenesis and growth of dominant follicles.

STAT4 targets KISS1 to promote the apoptosis of ovarian granulosa cells

Background

In mammals, it is known that the estradiol-17β (E2) is mainly synthetized in ovarian granulosa cells (GCs), and the excessive apoptosis of GCs induces the follicular atresia. Many studies have implicated the essential role of KISS1, with the pro-synthetic effect of E2 and the anti-apoptotic effect on GCs, in the mammalian folliculogenesis, and several STAT4 potential binding sites were previously predicted on the promoter of KISS1 in pigs. However, the biological effects of STAT4 on GCs and the molecular regulation between STAT4 and KISS1 remained largely unknown.

Methods

Using the porcine GCs as the cellular model, the overexpression plasmid, small interfering RNA, 5′-deletion and luciferase assay were applied to investigate the molecular mechanisms for STAT4 regulating the expression of KISS1.

Results

In this study, the STAT4 negatively regulated the mRNA and protein levels of KISS1 in porcine GCs, and the mRNA level of STAT4 was observed to significantly decrease from immature to mature follicles, which was inversed with that of KISS1. The relative luciferase activity of KISS1 promoter was significantly increased with deletion of the fourth potential binding site (− 305/− 295), and ChIP further confirmed that the STAT4 bound at − 305/− 295 region of KISS1. Besides, the STAT4 significantly regulated the mRNA levels of PDK1, FOXO3 and TSC2 of PI3K signaling pathway to promote the cell apoptosis and the percentage of cells at G0/G1 phase of cell cycle in GCs. Alternatively, the STAT4 significantly decreased the mRNA levels of CYP17, 3B-HSD, 17B-33 HSD, ESR1, and ESR2, as well as the concentration of E2 in GCs. Furthermore, interfering with the expression of STAT4 was observed to significantly stimulate the pro-synthetic effect of E2 and anti-apoptotic effect of KISS1 in GCs.

Conclusions

Collectively, the STAT4 might directly target at − 305/− 295 region of KISS1 to negatively regulate the transcription of KISS1, promote the cell apoptosis via PI3K signaling pathway, suppress the synthesis of E2 through the estrogen signaling pathway in porcine GCs. These proposed works could provide useful insight in further investigations on the molecular functionalities of STAT4 and KISS1 in the folliculogenesis of mammals.

Regulation of AMH, AMHR-II, and BMPs (2,6) Genes of Bovine Granulosa Cells Treated with Exogenous FSH and Their Association with Protein Hormones

Anti-Mullerian hormone (AMH) is an important reproductive marker of ovarian reserve produced by granulosa cells (GCs) of pre-antral and early-antral ovarian follicles in several species, including cattle. This hormone plays a vital role during the recruitment of primordial follicles and follicle stimulating hormone (FSH)-dependent follicular growth. However, the regulatory mechanism of AMH expression in follicles is still unclear. In this study, we compared the expression of AMH, AMHR-II, BMP2, BMP6, FSHR, and LHCGR genes during follicular development. In-vitro expression study was performed with and without FSH for AMH, AMHR-II, BMP2, and BMP6 genes in bovine GCs which were isolated from 3-8 mm follicles. Association among the mRNA expression and hormone level was estimated. GCs were collected from small (3-8 mm), medium (9-12 mm) and large size (13 to 24 mm) follicles before, during onset, and after deviation, respectively. Further, mRNA expression, hormones (AMH, FSH, and LH), apoptosis of GCs, and cell viability were detected by qRT-PCR, ELISA, flow cytometry, and spectrophotometry. AMH, AMHR-II, BMP2, and FSHR genes were highly expressed in small and medium follicles as compared to large ones. In addition, the highest level of AMH protein (84.14 ± 5.41 ng/mL) was found in medium-size follicles. Lower doses of FSH increased the viability of bovine GCs while higher doses repressed them. In-vitro cultured GCs treated with FSH significantly increased the AMH, AMHR-II, and BMP2 expression levels at lower doses, while expression levels decreased at higher doses. We found an optimum level of FSH (25 ng/mL) which can significantly enhance AMH and BMP2 abundance (p < 0.05). In summary, AMH, AMHR-II, and BMP2 genes showed a higher expression in follicles developed in the presence of FSH. However, lower doses of FSH demonstrated a stimulatory effect on AMH and BMP2 expression, while expression started to decline at the maximum dose. In this study, we have provided a better understanding of the mechanisms regulating AMH, AMHR II, and BMP2 signaling in GCs during folliculogenesis, which would improve the outcomes of conventional assisted reproductive technologies (ARTs), such as superovulation and oestrus synchronization in bovines.

New STAT3-FOXL2 pathway and its function in cancer cells

BACKGROUND

The forkhead transcription factor (FOXL2) plays a crucial role in blepharophimosis-ptosis-epicanthus inversus syndrome (BPES), sex determination, ovary growth and development, and cell cycle regulation. Emerging investigations have focused on the downstream targets of FOXL2, while little is known about its upstream regulation.

RESULTS

In this study, we show that FOXL2 could be regulated by STAT3 in cancer cells and that STAT3 binds to FOXL2 at the 5'- GCCTGATGTTTGTCTTCCCAGTCTGTGGCAA-3' site using EMSA and ChIP. We further found that knockdown of STAT3 or FOXL2 could significantly induce cancer cell apoptosis, indicating the importance of these two genes in cancer cell growth and apoptosis. Our data also indicated that the increased apoptotic cell rate may be caused by changes in apoptosis-related genes, such as TNF, TRAIL and GnRHR.

CONCLUSION

This study presents a new upstream regulator of FOXL2 and demonstrats that this new STAT3-FOXL2 pathway has an important function in HeLaHeLa cell apoptosis, providing new insights regarding the targeting of FOXL2 for cancer prevention and treatment.

Protective effects of trehalose on frozen-thawed ovarian granulosa cells of cattle

In this study, trehalose was investigated for its cryoprotective effects on ovarian granulosa cells (bGCs) of cattle. Five concentrations of trehalose at 0, 0.2, 0.4, 0.6 and 0.8 mol/L were added to the cryopreservation medium of bGCs, and the effects on the quality of frozen-thawed bGCs were assessed. The results indicate that the use of cryopreservation medium containing 0.2 and 0.4 mol/L of trehalose resulted in a greater rate of bGC viability compared to those of other groups (P<0.05). Culturing with trehalose at 0.2 and 0.4 mol/L increased 17β- estradiol (E₂)and decreased progesterone (P₄)production (P < 0.05) in post-thawed bGCs. Compared with the control group, the intracellular Ca²⁺ concentrations of frozen-thawed bGCs were less in all treatment groups (P<0.05), and the least Ca²⁺ concentration was observed in the group containing 0.4 mol/L trehalose. The plasma membrane potentials of frozen-thawed bGCs were greater in the groups with 0.2 and 0.4 mol/L trehalose, and the group treated with 0.4 mol/L trehalose had the greatest membrane potential in comparison to other groups (P < 0.05). The relative abundance of the CYP19 mRNA in frozen-thawed bGCs was greater in the groups containing 0.2, 0.4 and 0.6 mol/L trehalose, and relative abundances of FSHR and BCL2 mRNA were greater in the group of bGCs treated with 0.2 mol/L trehalose (P<0.05). Trehalose treatment at 0.4, 0.6 and 0.8 mol/L had an inhibitory effect on BAX gene transcription in frozen-thawed bGCs (P<0.05). In summary, trehalose exhibited a greater cryoprotective effect on bGCs than basic cryopreservation medium.

Luteinizing hormone upregulates NPPC and downregulates NPR3 mRNA abundance in bovine granulosa cells through activation of the EGF receptor

During folliculogenesis, the luteinizing hormone (LH) surge triggers dynamic events in granulosa cells that culminate with ovulation. The aim of this study was to evaluate if the epidermal growth factor receptor (EGFR) is required for ovulation in cattle, and if it regulates the expression of the natriuretic peptide (NP) system in granulosa cells after gonadotropin-releasing hormone (GnRH)/LH stimulation. It was observed that GnRH induces amphiregulin (AREG) and epiregulin (EREG) mRNA at 3 and 6 h after in vivo treatment, but the expression of these genes was not regulated by atrial (ANP) and C-type (CNP) NPs in granulosa cells cultured in vitro. The abundance of mRNA encoding the NP receptors (NPR1, 2 and 3) was not altered by LH supplementation and/or EGFR inhibition (AG1478; AG) in granulosa cells after 6 h of in vitro culture. However, in the same conditions, mRNA encoding the natriuretic peptide precursor C (NPPC) was upregulated by LH, whereas AG (0.5 and 5 μM) inhibited the LH effect. In order to confirm those results, 5 μM AG or saline were intrafollicularly injected in preovulatory follicles and cows were simultaneously treated with GnRH intramuscularly. Granulosa cells harvested at 6 h after GnRH injection revealed higher NPR3 and lower NPPC mRNA levels in AG-treated, compared to control cows. However, intrafollicular injection of AG did not inhibit GnRH-induced ovulation. In granulosa cells cultured in vitro, ANP associated with LH increased prostaglandin-endoperoxide synthase 2 (PTGS2) mRNA abundance. In conclusion, we inferred that LH modulated NPPC and NPR3 mRNA abundance through EGFR in bovine granulosa cells, but ovulation in cattle did not seem to depend on EGFR activation.

C/EBPβ Promotes STAT3 Expression and Affects Cell Apoptosis and Proliferation in Porcine Ovarian Granulosa Cells

Previous studies suggest that signal transducer and activator of transcription 3 (STAT3) and CCAAT/enhancer binding protein beta (C/EBPβ) play an essential role in ovarian granulosa cells (GCs) for mammalian follicular development. Several C/EBPβ putative binding sites were previously predicted on the STAT3 promoter in mammals. However, the molecular regulation of C/EBPβ on STAT3 and their effects on cell proliferation and apoptosis remain virtually unexplored in GCs. Using porcine GCs as a model, the 5′-deletion, luciferase report assay, mutation, chromatin immunoprecipitation, Annexin-V/PI staining and EdU assays were applied to investigate the molecular mechanism for C/EBPβ regulating the expression of STAT3 and their effects on the cell proliferation and apoptosis ability. We found that over and interfering with the expression of C/EBPβ significantly increased and decreased the messenger RNA (mRNA) and protein levels of STAT3, respectively. The dual luciferase reporter assay showed that C/EBPβ directly bound at −1397/−1387 of STAT3 to positively regulate the mRNA and protein expressions of STAT3. Both C/EBPβ and STAT3 were observed to inhibit cell apoptosis and promote cell proliferation. Furthermore, C/EBPβ might enhance the antiapoptotic and pro-proliferative effects of STAT3. These results would be of great insight in further exploring the molecular mechanism of C/EBPβ and STAT3 on the function of GCs and the development of ovarian follicles in mammals.

Natriuretic peptide system regulation in granulosa cells during follicle deviation and ovulation in cattle

Natriuretic peptides (NPs) are known to regulate reproductive events in polyovulatory species, but their function and regulation in monovulatory species remain to be fully characterized. Using a well-established in vivo model, we found that bovine granulosa cells from follicles near the deviation stage express mRNA for the three NP receptors (NPR1, NPR2 and NPR3), but not for NP precursors (NPPA, NPPB and NPPC). The abundance of NPR3 mRNA was higher in dominant compared to subordinate follicles at the expected time of follicular deviation. After deviation, mRNA for all NP receptors was significantly more abundant in the dominant follicle. Intrafollicular inhibition of oestrogen receptors downregulated NPR1 mRNA in dominant follicles. In granulosa cells from preovulatory follicles, NPPC mRNA increased at 3 and 6 h after systemic GnRH treatment, but decreased at 12 and 24 h to similar levels observed in samples collected at 0 h. After GnRH treatment, NPR1 mRNA was upregulated at 24 h, NPR3 mRNA gradually decreased after 3 h, while NPR2 mRNA was not regulated. The mRNA expression of the enzyme FURIN increased at 24 h after GnRH treatment. These findings revealed that the expression of mRNA encoding important components of the NP system is regulated in bovine granulosa cells during follicular deviation and in response to GnRH treatment, which suggests a role of NP system in the modulation of these processes in monovulatory species.

MicroRNA Mediating Networks in Granulosa Cells Associated with Ovarian Follicular Development

Ovaries, which provide a place for follicular development and oocyte maturation, are important organs in female mammals. Follicular development is complicated physiological progress mediated by various regulatory factors including microRNAs (miRNAs). To demonstrate the role of miRNAs in follicular development, this study analyzed the expression patterns of miRNAs in granulosa cells through investigating three previous datasets generated by Illumina miRNA deep sequencing. Furthermore, via bioinformatic analyses, we dissected the associated functional networks of the observed significant miRNAs, in terms of interacting with signal pathways and transcription factors. During the growth and selection of dominant follicles, 15 dysregulated miRNAs and 139 associated pathways were screened out. In comparison of different styles of follicles, 7 commonly abundant miRNAs and 195 pathways, as well as 10 differentially expressed miRNAs and 117 pathways in dominant follicles in comparison with subordinate follicles, were collected. Furthermore, SMAD2 was identified as a hub factor in regulating follicular development. The regulation of miR-26a/b on smad2 messenger RNA has been further testified by real time PCR. In conclusion, we established functional networks which play critical roles in follicular development including pivotal miRNAs, pathways, and transcription factors, which contributed to the further investigation about miRNAs associated with mammalian follicular development.

Differential regulation of Janus kinase 3 (JAK3) in bovine preovulatory follicles and identification of JAK3 interacting proteins in granulosa cells

Background

Janus kinase 3 (JAK3) is a member of the membrane-associated non-receptor tyrosine kinase protein family and is considered predominantly expressed in hematopoietic cells. We previously identified JAK3 as a differentially expressed gene in granulosa cells (GC) of bovine preovulatory follicles. The present study aimed to further investigate JAK3 regulation, to identify protein binding partners and better understand its mode of action in bovine reproductive cells.

Results

GC were obtained from small follicles (SF), dominant follicles at day 5 of the estrous cycle (DF), and ovulatory follicles, 24 h following hCG injection (OF). RT-PCR analyses showed greatest expression of JAK3 in GC of DF, while JAK3 expression was downregulated in OF (P < 0.0001). In addition, there was a 5- and 20-fold reduction of JAK3 steady-state mRNA levels in follicular walls, respectively at 12 and 24 hours post-hCG as compared to 0 h (P < 0.05). Similarly, JAK3 expression was downregulated by the endogenous LH surge. These results were confirmed in western blot analysis showing weakest JAK3 protein amounts in OF as compared to DF. Yeast two-hybrid screening of a DF-cDNA library resulted in the identification of JAK3 partners in GC that were confirmed by co-immunoprecipitation and included leptin receptor overlapping transcript-like 1 (LEPROTL1), inhibin beta A (INHBA) and cyclin-dependent kinase inhibitor 1B (CDKN1B). In functional studies using bovine endometrial cells, JAK3 increased phosphorylation of STAT3 and cell viability, while the addition of JANEX-1 inhibited JAK3 actions.

Conclusion

These results support a physiologically relevant role of JAK3 in follicular development and provide insights into the mode of action and function of JAK3 in reproductive tissues.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-016-0280-5) contains supplementary material, which is available to authorized users.

The theory of follicle selection in cattle

Selection of the dominant follicle (DF) during a follicular wave is manifested by diameter deviation or continued growth rate of the largest follicle (F1) and decreased growth rate of the next largest follicle (F2) when F1 reaches about 8.5 mm in cattle. The process of deviation in the future DF begins about 12 h before diameter deviation and involves an F1 increase in granulosa LH receptors and estradiol and maintenance of intrafollicular free insulin-like growth factor 1 (IGF1). Thereby, only F1 is developmentally prepared to use the declining FSH in the wave-stimulating FSH surge and to respond to a transient increase in LH to become the DF. A follicle that emerges first may maintain an F1 ranking and become the DF by being first to reach a critical developmental stage. However, an early size advantage is not a requisite component of the deviation process as indicated by (1) F1 and F2 may switch diameter rankings during a common growth phase that precedes diameter deviation owing to intraovarian factors that affect growth of individual follicles; (2) any follicle that reaches 5 mm regardless of diameter ranking may become a DF unless it is selected against during deviation; (3) a subordinate follicle may become dominant if the DF is ablated; (4) when F1 is ablated at 8.5 mm, the next largest follicle that is greater than 7.0 mm or the first follicle to subsequently reach 7.0 mm becomes the DF; (5) after ablation of F1 at 8.5 mm, IGF1 and estradiol increase in the intrafollicular fluid of F2 beginning at 6 h, and F2 grows to 8.5 mm in 12 h to become the DF. These considerations indicate that selection of a DF or partitioning into a DF and subordinate follicles is not initiated before the end of the common growth phase. That is, the deviation process represents the entire follicle selection mechanism.

Lack of FSH support enhances LIF-STAT3 signaling in granulosa cells of atretic follicles in cattle

Subordinate follicles (SFs) of bovine follicular waves undergo atresia due to declining FSH concentrations; however, the signalling mechanisms have not been fully deciphered. We used an FSH-induced co-dominance model to determine the effect of FSH on signalling pathways in granulosa cells of the second-largest follicles (SF in control cows and co-dominant follicle (co-DF2) in FSH-treated cows). The SF was smaller than DF in control cows while diameters of co-DF1 and co-DF2 in FSH-treated cows were similar. The presence of cleaved CASP3 protein confirmed that granulosa cells of SFs, but not of DFs and co-DFs, were apoptotic. To determine the effect of FSH on molecular characteristics of the second-largest follicles, we generated relative variables for the second largest follicle in each cow. For this, variables of SF or co-DF2 were divided by the variables of the largest follicle DF or co-DF1 in each cow. There was higher transcript abundance of MAPK1/3 and AKT1/2/3 but lower abundance of phosphorylated MAPK3/1 in SF than co-DF2 granulosa cells. Abundance of mRNA and phosphorylated protein of STAT3 was higher in granulosa cells of control SF than FSH-treated co-DF2. SF granulosa cells had higher levels of LIFR and IL6ST transcripts, the two receptors involved in STAT3 activation. Further, lower transcript abundance of interleukin 6 receptor (IL6R), another receptor involved in STAT3 activation, indicated that STAT3 activation in SF granulosa cells could be mainly due to leukemia inhibitory factor (LIF) signalling. These results indicate that atresia due to lack of FSH is associated with activated LIF-STAT3 signalling in SF granulosa cells, as FSH treatment reversed such activation.

Regulation of Anti-Müllerian Hormone and Its Receptor Expression around Follicle Deviation in Cattle

The anti-Müllerian hormone (AMH) is an important marker of ovarian reserve and for predicting the response to superovulatory treatments in several species. The objective of this study was to investigate whether AMH and its receptor (AMHR2) are regulated in bovine granulosa cells during follicular development. In the first experiment, granulosa cells were retrieved from the two largest follicles on days 2 (before), 3 (at the expected time) or 4 (after deviation) of follicular wave. In the second experiment, four doses of FSH (30, 30, 20 and 20 mg) or saline were administered twice a day starting on Day 2 of the first follicular wave of the cycle. Granulosa cells and follicular fluid were collected from the two largest follicles 12 h after the last injection of FSH or saline. AMH mRNA abundance was similar in granulosa cells of the two largest follicles (F1 and F2) before deviation (Day 2), but greater in dominant (DF) than subordinate follicles (SF) at the expected time (Day 3) and after (Day 4) deviation (p < 0.05). In experiment 1, AMH mRNA levels declined in both DF and SF near the expected time and after deviation when compared to before deviation. There was no difference in AMHR2 mRNA levels before and during follicular deviation (p > 0.05), but they tended to be greater in DFs than SFs (p < 0.1) after deviation. Experiment 2 showed that AMH and AMHR2 mRNA in granulosa cells and AMH protein abundance in follicular fluid were similar (p > 0.05) between both co-dominant follicles collected from the FSH-treated cows. These findings indicate the followings: AMH mRNA levels decrease in both DFs and SFs during follicular deviation; granulosa cells from heathy follicles express more AMH mRNA compared to subordinate follicles undergoing atresia and FSH stimulates AMH and AMHR2 mRNA expression in granulosa cells of co-dominant follicles.